The present invention relates to a filtration apparatus useful for peridural or epidural anesthesia. Peridural or epidural anesthesia are a type of locoregional anesthesia currently used in treating pain, especially for chronic illnesses, surgical operations and childbirth. In this procedure, the practitioner should first locate the peridural space, where the spinal nerve to be anesthetized is found, by introducing the end of a bevelled peridural needle upward between the second and third lumbar vertebrae. This beveled end emerges into the peridural space deliminated by the dura matter and the walls of the spinal canal. A flexible catheter then is introduced through this needle, in order to deliver the anesthetic into the space.
In order to avoid any bacterial and microparticular (glass, rubber, etc.) contamination arising from the transfer of the anesthetic, it is imperative to effect a filtration through a device located downstream from the syringe delivering the anesthetic and upstream from the catheter.
At the present time, two different filter assemblies for peridural anesthesia are available. A first type consists of a circular filtering membrane, the periphery of which is joined to an envelope of plastic material in two parts, located on either side of the membrane; each of these two parts has an enclosed space equipped with an inlet or outlet opening. The axis of the enclosed space is perpendicular to the plane of the filtering membrane. This first type of filter is not suitable in practice due to its structure having a top surface which prevents it fixation in a convenient and comfortable manner to the body of the patient being treated.
A second type of filter differs from the first type in that the axes of the inlet and outlet orifices to spaces located on either side of the filtering membrane are arranged, not perpendicularly, but in parallel to the plane of this membrane; itself parallel to the filtration case. However, in this second filter type the inlet and outlet openings project from the same side of the membrane, which presents a double disadvantage. Such an arrangement permits fixing the filter on the body of the patient on only one side, i.e., the side opposite that from which the access openings to the membrane project. Also, because the two openings are located on the same side of the membrane, a "U" shaped access channel to the opposite side of the membrane must be provided for one of them which necessitates the presence of a third, circular crown-shaped plastic element in order to delimit this access channel. A structure with three plastic elements increases the cost of manufacturing this filter type and, furthermore, due to the U-shape of the access channel to one of the sides of the membranes, creates a pressure drop that reduces the sensitivity of the apparatus during use by the anesthetist.